Lupus nephritis is caused by pathogenic autoantibodies (Abs) that are T-cell dependent. In NZB/NZW Fl (BW) mice, and in patients, some Abs deposited in glomeruli bear a public Id designated 1d6N2. The investigators hypothesize that B-cells producing Ids enriched in pathogens are upregulated by helper T-cells (TH) which are activated by complementary Id structures. The investigators developed and are characterizing BW monoclonal (Mab) Abs to dsDNA with regard to pathogenicity (in vitro), isotype, charge, complement- fixing abilities, epitope specificity, and Id expression. Four are 1dGN2+ 1gG2a high avidity anti-dsDNA; two accelerate nephritis in young BWs, two do not. Several BW L3T4+, Ly2-TH have been cloned and are being characterized for MHC restriction, proliferative responses to DNA, Id and anti-Ids, lymphokine profiles, ability to regulate production of various lds by unprimed BW B-cells in vitro, and ability to alter Ids, anti-Ids and disease in vitro. Two TH (Mosmann Class 2) cells that upreguate production of 1dGN2 accelerate nephritis; one TH (Mosmann 1) does not upregulate 1dGN2 or accelerate disease. Based on these observations, the investigators propose three studies. 1) Define the structures which determine expression of various public Ids on V regions of Ig molecules, by sequencing of H and L chain V regions, modeling the Ag-binding groove, and developing mutant H and/or L chains to separate Id expression and Ag-binding. Correlations will be made between pathogenicity and differences in structure, Id, epitope specificity, etc. 2) Define the structures recognized by IdTH, most likely peptides presented by MHC on B-cells. Synthetic peptides will be used to stimulate TH and to inhibit in vitro interactions between BW B and IdTH. Wild and mutant Ig molecules will also be presented to IdTH by B-cells to determine the structure of Ids recognized by TH. 3) Based on results of 1 and 2, the investigators will test interventions designed to inactivate various IdTH that support production of pathogenic Abs. Two approaches will be used - Mabs against TcR of IdTH, and tolerization with peptides. The overall objective is to understand a mechanism contributing to disease and develop interventions that result in specific suppression of pathogenic Ab subsets.